One of the biggest challenges of fused deposition modeling (FDM)/fused filament fabrication (FFF) 3D-printing is maintaining consistent quality of layer-to-layer adhesion, and on the larger scale, homogeneity of material inside the whole printed object. An approach for mitigating and/or resolving those problems, based on the rapid and reliable control of the extruded material temperature during the printing process, was proposed. High frequency induction heating of the nozzle with a minimum mass (<1 g) was used. To ensure the required dynamic characteristics of heating and cooling processes in a high power (peak power > 300 W) heating system, an indirect (eddy current) temperature measurement method was proposed. It is based on dynamic analysis over various temperature-dependent parameters directly in the process of heating. To ensure better temperature measurement accuracy, a series-parallel resonant circuit containing an induction heating coil, an approach of desired signal detection, algorithms for digital signal processing and a regression model that determines the dependence of the desired signal on temperature and magnetic field strength were proposed. The testbed system designed to confirm the results of the conducted research showed the effectiveness of the proposed indirect measurement method. With an accuracy of ±3 °C, the measurement time is 20 ms in the operating temperature range from 50 to 350 °C. The designed temperature control system based on an indirect measurement method will provide high mechanical properties and consistent quality of printed objects.

Рассмотрены наиболее эффективные технологии аддитивного производства металлических изделий, использующие методы послойного нанесения материала. Описаны принципы работы таких технологий, как GMAW, GTAW, PAW, CMT, DMD, LBDMD, EBAM, FDM. Приведена сводная таблица ключевых характеристик данных процессов, и представлен их сравнительный анализ. Выявлены преимущества и недостатки данных методов, основные области применения и тенденции развития. Определено наиболее перспективное направление развития технологий создания металлических изделий методом послойного нанесения материала. Сделан вывод о том, что технология FDM далеко не полностью раскрыла свой потенциал из-за широкого спектра технических проблем. Рассмотрены текущие исследования, направленные на преодоление существующих технологических барьеров, препятствующих развитию FDM технологии 3D-печати. Рассмотрен круг вопросов, на которые необходимо ответить для успешного изготовления металлических изделий при помощи данной технологии. Выдвинуты гипотезы, и найдены пути решения проблем. Рассмотрены перспективы данной технологии, а также дана оценка ее полезности в производстве и для общества. Представлен начальный этап разработки научным коллективом Пермского национального исследовательского политехнического университета более мобильной и легкодоступной технологии печати металлических изделий сложной геометрической формы на основе FDM технологии 3D-печати. Описан ряд технических решений, позволяющих обойти или решить существующие проблемы и ограничения, действующие в данной области. Например, разогрев горячей части экструдера до 1000 °C за несколько десятков секунд и ранее невозможный быстрый и точный контроль температуры, позволяющий полностью контролировать процесс экструзии материала.

This article addresses the problem of induction heating in its application to the FDM/FFF 3D manufacturing. One of the major problems of the FDM/FFF is the instability of layer-to-layer adhesion quality, and on the larger scale - maintaining the homogeneity of material inside the whole printed object. Approach for mitigating and/or resolving of those problems, based on the fast and reliable control of the extruded material temperature during the printing process was proposed. Such approach uses specially created testbed system, consists of the ultra-low weight induction heated nozzle and fast temperature controller. This equipment enables rapid heating and cooling of the nozzle at low input power. On the contrary, using of the nozzle with the minimal thermal mass poses the problems of maintaining even heat distribution on the nozzle surface, and therefore inside the heated material. Multiphysics FEM model for the electromagnetic and thermal problem for the proposed nozzle and inductor configuration was formulated, and numerically solved using COMSOL 5.2a. Parametric optimization of the inductor form and heating signal frequency was conducted. Series of the experiments with the optimized inductor construction were made using the proposed testbed, showing significant increase of the heating speed and uniform heat distribution on the nozzle surface, and therefore in the final printed object quality. Experimental data for the all stages of conducted research is provided.

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An approach for improving and maintaining consistent fusion quality of the deposited material during FDM 3d-printing is proposed. This approach is based on the nozzle temperature control during the printing process to adjust the polymer extrusion temperature with a speed and accuracy adequate to the FDM process. High frequency induction heating of the lightweight nozzle (<1 g) was used. To control the temperature of a lightweight nozzle, the resonant temperature measurement method based on the analysis of the high frequency eddy currents is proposed. To determine the parameters of the nozzle and the inductor as a plant, a FEM model of the inductive heating of the nozzle and a simulated model of a serial-parallel resonant circuit containing inductor were developed. Linearization of the automatic control system was performed to ensure the equal quality of regulation when operating in a wide temperature range. The quality of regulation, stability of the system, and coefficients of the PID controller were evaluated using a simulated model of the control system. A number of test samples were printed from various materials, and tensile stress testing was carried out. The developed control method reduces the nozzle temperature control error from 20 to 0.2 °C and decreases control delay by more than six times.